Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from Polyethylene Teraphalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material involves heating the molding material (ex. PET pellets, etc.) to a homogeneous molten state and injecting, under pressure, the so-melted PET material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of the mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be demolded, i.e. ejected off of the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, ejector pins, etc.
When dealing with molding a preform that is capable of being blown into a beverage container, one consideration that needs to be addressed is forming a so-called “neck portion”. Typically and as an example, the neck portion includes (i) threads (or other suitable structure) for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an anti-pilferage assembly configured to cooperate, for example, with the closure assembly to indicate whether the end product (i.e. the beverage container that has been filled with a beverage and shipped to a store) has been tampered with in any way. The neck portion may comprise other additional elements used for various purposes, for example, to cooperate with parts of the molding system (ex. a support ledge, etc.). As is appreciated in the art, the neck portion can not be easily formed by using the cavity and core halves. Traditionally, split mold inserts (sometimes referred to by those skilled in the art as “neck rings”) have been used to form the neck portion.
With reference to FIG. 1, a section along a portion of an injection mold 50 illustrates a portion of typical molding insert stack assembly 60 that is arranged within a molding system (not depicted). The description of FIG. 1 that will be presented herein below will be greatly simplified, as it is expected that one skilled in the art will appreciate general configuration of other components of the injection mold 50 that will not be discussed in the following description.
The molding insert stack assembly 60 includes a neck ring insert pair 52 that together with a mold cavity insert 54, a gate insert (not shown) and a core insert 61 define a molding cavity (not separately numbered) where molding material can be injected to form a molded article, such as a perform 63. In order to facilitate forming of the neck portion of the preform 63 and subsequent removal of the preform 63, the neck ring insert pair 52 comprises a pair of complementary neck ring inserts that are mounted on adjacent slides of a slide pair 68. The slide pair 68 is slidably mounted on a top surface of a stripper plate 66. As commonly known, and as, for example, generally described in U.S. Pat. No. 6,799,962 to Mai et al (granted on Oct. 5, 2004), the stripper plate 66 is configured to be movable relative to a cavity plate assembly 74 and a core plate assembly (not depicted), when the mold is arranged in an open configuration, whereby the slide pair 68, and the complementary neck ring insert pair 52 mounted thereon, can be laterally driven, via a cam arrangement or some other means (not shown), for the release of the molded article from the molding cavity.
A typical neck ring insert has a body that includes a pair of projecting portions 70 that extend from a top and a bottom face of a flange portion 72 (i.e. a top projecting portion and a bottom projecting portion). Typically, the bottom face of the flange portion 72 abuts, in use, a top surface of the slide pair 68. Even though not depicted in FIG. 1, one skilled in the art will appreciate that the neck ring insert pair 52 cooperates with suitable fasteners for connecting to a respective one of the slide pair 68. In use, during certain portions of a molding cycle, the top projecting portion cooperates with a female receptacle disposed on the cavity plate assembly 74.
FIG. 2 depicts an example of a prior art implementation of a neck ring 200 of the neck ring insert pair 52. More specifically, FIG. 2 depicts a front planar view of the neck ring 200. The neck ring 200 comprises a molding surface 202 for forming, in use, various portions of the neck finish of the preform and a mating surface 204 for abutting, in use, another one of the neck ring 200. The neck ring 200 further includes a venting structure 206. The venting structure 206 comprises (i) an air vent groove 208 for collecting and venting, in use, excess air from the molding cavity as it is being filled with the molding material and (ii) an air collector groove 210 in fluid communication with the air vent groove 208 for providing an evacuation path for the air to be vented from the air collector groove 210.
US patent application 2008/0026239 published to Alessandro, et al. on Jan. 31, 2008 discloses a preform that is formed by an upper neck which maintains unchanged its form in the final object and a hollow body, joined to the neck. The method foresees the insertion, within a matrix cavity, of a metered body of polymeric material whose mass is metered according to a reference value, and the subsequent pressure insertion of a punch within the matrix cavity until it closes the mold's molding chamber, the punch conferring the shape to the inner surface of the preform and the matrix having an inner surface which confers the shape to the outer surface of the preform. According to the invention, in the molding of the preform, the error of the mass of the metered body with respect to the reference value is distributed in the hollow body, which undergoes a subsequent hot deformation until it achieves the final shape. In the mold, the matrix comprises at least one deformable wall (31) whose inner surface defines at least part of the inner surface of the matrix part intended to give form to the hollow body of the preform, said deformable wall (31) having, at least in part, a relatively thin thickness which permits it to be elastically deformed under the pressure of the polymeric material in the final preform molding step, thereby varying the thickness of the hollow body.
U.S. Pat. No. 7,128,865 issued to Martin on Oct. 31, 2006 discloses an injection molding method and apparatus for ejecting a molded plastic preform from a mold. A first lifting structure and/or step is configured to have an inner surface with an area for sealing and aligning with a complementary surface on a core, and to have an upper surface with an area for sealing and aligning with a complementary surface on a second lifting structure, said upper surface of said first lifting structure being configured to lift a molded plastic preform from the injection mold in a lifting direction for a first period of time, the lower portion of the molded plastic preform lying in a plane substantially perpendicular to the lifting direction. A second lifting structure and/or step is configured to have an inner surface configured to lift an outer surface of the molded plastic preform from the injection mold in the lifting direction for a second period of time, the outer surface of the molded plastic preform including structure lying in a plane substantially parallel with the lifting direction. Since the molded plastic preform is lifted by its end, the preform does not have to be solidified at its interior, thus allowing earlier removal of the preform from the mold, reducing cycle time.